Disc drive systems have been used in computers and other electronic devices for many years for storage of digital information. Information is recorded on concentric memory tracks of a magnetic disc medium, the actual information being stored in the form of magnetic transitions within the medium. The discs themselves are rotatably mounted on a spindle, the information being accessed by means of transducers located on a pivoting arm which moves radially over the surface of the disc. The read/write heads or transducers must be accurately aligned with the storage tracks on the disc to ensure proper reading and writing of information; thus the discs must be rotationally stable.
Electric spindle motors of the type used in disk drives conventionally rely on ball bearings to support a rotary member, such as a rotating hub, on a stationary member, such as a shaft. Ball bearings are known to wear parts, and in time increased friction will cause failure of the motor. In addition, ball bearings create debris in the form of dust or fine particles that can find their way into “clean” chambers housing the rotary magnetic disks which are driven by the motor. The mechanical friction inherent in ball bearings also generates heat, noise and vibration, all of which are undesirable in a disk drive motor.
Hydrodynamic bearings represent a considerable improvement over conventional ball bearings in spindle drive motors. In these types of systems, lubricating fluid, either gas or liquid, functions as the actual bearing surface between a stationary base or housing in the rotating spindle or rotating hub of the motor. For example, liquid lubricants comprising oil, more complex ferro-magnetic fluids or even air have been utilized in hydrodynamic bearing systems.
Hydrodynamic bearings have the advantage over ball bearings of improved running precision, greater shock resistance and lower noise generation.
Spindle motors for data carrier disks, in which a shaft fixedly mounted on a rotor has a hydrodynamic bearing system, are known in the art. A hydrodynamic bearing system according to the prior art consists, for example, of a bearing sleeve which can be enclosed at one end by a counter plate. The shaft is placed within the bearing sleeve and is enveloped in a fluid, preferably oil. Either the inner surface of the bearing sleeve or the outer surface of the shaft, a plurality of groove patterns are provided which generate radial hydrodynamic bearing pressure when the shaft is rotated.
Furthermore, hydrodynamic bearings with axial pivot bearings in low-power spindle motors are also known, in which axial bearing loads are taken up in one direction on a counter plate by supporting the bearing at the center of rotation and in which the axial counter load is generated magnetically, for example, by the interaction of the rotor and stator. These types of hydrodynamic bearings, however, have very low axial stiffness and their use, for example in hard disk drives, is problematic since such applications require axial stiffness in both axial directions. On the other hand, hydrodynamic bearings with axial pivot bearings have the advantage of very low frictional loss and consequently very low power consumption.
An example of a hydrodynamic bearing in accordance with the prior art as described above, is known from U.S. Pat. No. 4,934,836.
Hydrodynamic bearings are currently used in spindle motors for disk drives having very small dimensions, for example, in laptop computers. Spindle motors with hydrodynamic bearings for use in disk drives with small dimensions should have low power consumption, particularly when deployed in mobile, battery operated devices.
In the prior art, spindle motors with hydrodynamic bearings consist generally of a range of discrete separate components. Specifically, the bearing sleeve is non-rotatably mounted onto a flange, a baseplate, a frame, a support or suchlike of a spindle motor and the shaft is held in the bearing sleeve. In order to mount the bearing sleeve onto the flange or baseplate, these members typically feature a flange sleeve in which the bearing sleeve is non-rotatably held. The bearing sleeve and flange sleeve can be permanently connected together by bonding, welding, pressing or in any other manner.
High-precision machining and perfectly aligned assembly of the individual components are the key to the efficient and precise functioning of a hydrodynamic bearing. To construct a hydrodynamic bearing of the stated art, specific minimum wall thicknesses for the individual components are required, prescribed on the one hand by production techniques and on the other arising from the requirement for sufficient mechanical stability.